1. Field of the Invention
The present invention relates to a switching valve unit and an endoscope apparatus. More particularly, the present invention relates to a switching valve unit and an endoscope apparatus, in which failure in closing in a closed state between plural flow channels can be prevented, and operability of manual depression can be high.
2. Description Related to the Prior Art
An endoscope includes an elongated tube, and a tube channel or suction channel. The elongated tube is entered in a body cavity of a patient, for imaging an object of interest . The tube channel extends through the elongated tube to a suction opening at a distal end. A switching valve unit is disposed on a control handle of the endoscope. The tube channel is coupled to the switching valve unit. The tube channel is an instrument channel and also a suction channel. Namely, the tube channel is used for entry of a medical instrument, such as a forceps. Also, the tube channel is used for suction of fluid. The tube channel may have a structure with branches.
Plural conduits are coupled to the switching valve unit, including an exhaust conduit and the tube channel. The exhaust conduit extends to a suction source, such as a suction pump. The switching valve unit is changeable over by manipulation of depression between a closed state and a flow-through state. In the closed state, the tube channel is closed from communication with the exhaust conduit. In the flow-through state, the tube channel is caused to communicate with the exhaust conduit for enabling suction.
An example of the switching valve unit is a suction button unit, and includes a valve cylinder and a piston rod. The valve cylinder includes a piston chamber, a suction port hole and an exhaust port hole. The piston chamber has open ends. The suction port hole is disposed at a lower end of the piston chamber, and communicates with the tube channel. The exhaust port hole is formed through an inner surface of the piston chamber, and communicates with the exhaust conduit. The piston rod is received in the piston chamber, and is shiftable from a first position to a second position by manipulation of depression. The piston rod includes a side opening, an end opening and a flow path. The side opening becomes aligned with the exhaust port hole in case the piston rod is in the second position. The end opening is formed in a lower end, and communicates with the suction port hole. The flow path is formed to communicate between the side opening and the end opening.
U.S. Pat. No. 5,840,015 (corresponding to JP-A 8-252216) discloses the suction button unit in which seal packing is disposed around the side opening for preventing suction of the atmosphere through a gap space between the piston rod and the valve cylinder with negative pressure of the suction source in the flow-through state. In U.S. Pat. No. 5,840,015 and JP-A 2006-271890, the suction button unit is an O-ring and the like of a ring shape fitted on a lower end of the piston rod. JP-A 2004-223121 (corresponding to DE-B 10 2004 003857) discloses the suction button unit including a button cap, a cap device or cylinder cap, and the seal packing, arranged on the piston rod. The cap device is disposed on the valve cylinder and receives the button cap. The seal packing is so disposed that the cap device receives the button cap in case the piston rod is depressed for the flow-through state. The seal packing seals a gap space between the button cap and the cap device.
However, the seal packing of U.S. Pat. No. 5,840,015 and JP-A 2006-271890 has a problem of degradation. Response to manipulation of the depression to the piston rod may become poor, or return of the piston rod after interrupting the depression may be too slow, due to the degradation of the seal packing with time between the piston rod and the valve cylinder in the suction button unit. Furthermore, air of the atmosphere is likely to be drawn through a weakened portion of the seal packing by the suction in the suction button unit of U.S. Pat. No. 5,840,015 and JP-A 2006-271890. In JP-A 2004-223121, there is no suggestion of seal packing between the piston rod and the valve cylinder in the suction button unit. While the piston rod is in the first position for the closed state, negative pressure occurs in the tube channel through the flow path due to a fine gap space between an outer surface of the piston rod and an inner surface of the valve cylinder. Unwanted suction is likely to occur at the distal opening of the tube channel.